Probing intramolecular interactions using molecular electrostatic potentials: changing electron density contours to unveil both attractive and repulsive interactions
Résumé
We focus on intramolecular interactions, using the electrostatic potential plotted on iso-density
surfaces to lead the way. We show that plotting the electrostatic potential on varying iso-density
envelopes much closer to the nuclei than the commonly-used 0.001 a. u. contour can reveal the
driving forces for such interactions, whether they be stabilizing or destabilizing. Our approach
involves optimizing the structures of molecules exhibiting intramolecular interactions and then
finding the contour of the electronic density which allows the interacting atoms to be separated;
we call this the nearly-touching contour. The electrostatic potential allows then to identify the
intramolecular interactions as either attractive or repulsive. The discussed 1,5- and 1,6-
intramolecular interactions in o-bromophenol and o-nitrophenol are attractive, while the
interactions between terminal methyl hydrogens in diethyl disulfides (as shown recently) and
those between the closest hydrogens in planar biphenyl and phenanthrene are clearly repulsive
in nature. For the attractive 1,4-interactions in trinitromethane and chlorotrinitromethane, and
the 1,3-S---N and Si---O interactions in the ClH2Si(CH2)nNH2 series, the lack of (3,-1) bond
critical points was often cited as reason to not identify the 1,3-Si---N interactions as attractive
in nature. Here, by looking at the nearly-touching contours we see that bond critical points are
neither necessary nor sufficient for attractive interactions, as others have pointed out, and in
some instances also pointing to repulsive interactions, as the examples of planar biphenyl and
phenanthrene discussed in this work show
Domaines
Sciences du Vivant [q-bio]Origine | Fichiers produits par l'(les) auteur(s) |
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